Telephoto for Nex-3N

I was thinking about Tamron 18-200mm F/3.5-6.3 Di III VC for the Nex but then I thought, why not buy the Tamron AF 18-200mm F/3.5-6.3 XR Di II LD for 1/4 of the price and then some sort of adapter? Is this possible? Would it compromise some quality or functions? What adapter do I need?

The Sony LA-EA2 adapter is too much expensive. Even on eBay. I was thinking there was some low priced adapters that would do the job. If not, than there goes my idea...

Don't get me wrong, changing lenses in this case is not good for me. Or it's not possible. I need one all around lense for my next travel and I won't have the chance or be able to change lenses if and when I want to.

An adapted 18-200 Tamron might be more trouble than switching lenses.
The good adapters that allow for aperture changes are fairly expensive and
manually focusing without an EVF in the bright sun on the 3n will be tough.

Maybe a rental? The Sony 18-105 or 18-200 looks like it might fit the bill.
Or a second body. One with 16-50 and the other with the 55-210.

Jimphoto,
What sort of budget are you looking at? If you need autofocus, then your options in native E-mount lenses are somewhat limited for do-it-all zoom lenses. There is the SEL55210 which complements the kit SEL1650 from the NEX-3N well, picking up where it leaves off at around 50-55mm. For more full coverage, there is the Tamron 18-200 E-mount zoom that you mentioned. You might be able to find a good used copy on eBay, Amazon Marketplace, or KEH.com (in the US; others may know options outside the US). And then there are the two Sony 18-200s (well, there is a third, but it's a power zoom and much more expensive). The SEL18200LE looks a lot like the Tamron (some even claim it's made by Tamron), and the SEL18200 (non-LE version) looks larger, but is just as versatile, and seems to go for a bit less used as it's a slightly older model. You can find some at KEH.com at https://www.keh.com/search/list?pmnt=Sony+E+Mount&fl[]=18-200mm

If you are okay with manual focus, well, then your options for legacy manual focus lenses really opens up, and a lot of very good lenses can be found for under $300 easily. As mostly full-frame film-based lenses though, these legacy zooms generally don't come in the same wide-to-long range of the APS-C-based 18-200s. You can find some 24-105 and 28-200 range ones though.

I hope some of that helps a little. As a budget-focused hobbyist myself, I "feel your pain."

A big zoom lens designed for a DSLR, plus a heavy and large adapter? It wouldn't be a great travel setup anyway.

You'd be better off with the kit lens. The kit is usually long enough, and wide enough for most situations... and probably has higher image quality than that Tamron.

I'm only guessing, never tried the Tamron. I do know that all in one "superzoom" lenses are very rarely any good for image quality, too many compromises are needed to get that zoom range.

So yeah, the kit is fine

The exception is wildlife. If you are travelling and want to get shots of wildlife, well then you really should think about the 55-210mm. You won't have to swap lenses that often, you will know the days when that lens will make sense.

I had similar constraints, bought two different legacy lenses (spent ~ USD 140) and ultimately bought the Sony E 55-210mm lens. Whatever legacy lens you buy, it won't match up to this lens, mainly because of its OSS. This E Lens may not be great, but does the job adequately.

Legacy lenses could come very handy, if you have a NEX body with "View Finder" and mounted on a solid "Tripod". Without these two, it is difficult to pin point focus on the LCD in day light for focal lengths above 150mm, IMO. If you are not in the habit of carrying a tripod around, buying the SEL55210 would result in less expenditure in the long run.

PS: Had someone advised me the above, before I spent money on legacy zooms, I wouldn't have listened. I would still have wasted money on legacy zooms and ended up with SEL55210. Such is the human mind ....

I've really been happy with my new SEL18200LE, but as you say it is pretty expensive, especially when one of my objectives was a smallish system (but it's still way smaller than my D800 & AF-S 28-300).

Being a frugal guy, my only native E-mount lenses are the SEL1650 and SEL55210. The 1650 gets the most use. The SEL18200 would be tempting if the price were lower and I didn't already have the other two.
Since zoom lenses tend to perform worst at their zoom limits, I find it handy to have a legacy 50mm or 55mm legacy manual focus prime in the bag when I want a super sharp image at that focal length. Without an EVM manual focus would be difficult in daylight, but when light is low you get get images that are impossible with either of the other two.